Historical clue formulations

• Coin, commonly — 2026-05-24
• Component of the Tower of Hanoi puzzle — 2024-08-30
• Hockey puck, e.g. — 2021-05-03
• Plate, e.g. — 2020-10-16
• Shape of a U.F.O. — 2019-10-22
• Plate, e.g. — 2018-06-07
• Spine part — 2016-07-03
• U.F.O. shape — 2015-02-25
• It may slip in the back — 2013-09-06
• "Slipped" backbone part — 2009-12-28
• Poker chip, e.g. — 2006-01-29
• Tiddlywink, e.g. — 2004-09-07
• Part of the spine — 2004-04-12
• It's committed to memory — 2003-12-27
• Harrow blade — 2003-01-12
• Frisbee — 2002-10-14
• Floppy — 2000-04-07
• Frisbee — 1999-07-03
• Magnetic ___ — 1998-01-09
• Drive insert — 1996-02-22
• Computer insert — 1994-09-06